Gable Roof Metal Decking Calculator
Calculate roof area, rafter length, and trim requirements for gable roofs. Solves geometry based on floor pitch and dimensions. Includes waste factors for precise budgeting.
Bill of Materials Estimate
- Metal Decking: 0 sq.ft (inc. waste)
- Ridge Cap (10ft pcs): 0 pcs
- Rake Trim (10ft pcs): 0 pcs
About
A gable roof (dual-slope) is the most common residential roof form, yet calculating its surface area from a floor plan requires trigonometric application. Miscalculating the slope factor can lead to significant material shortages. This calculator solves the "hypotenuse" (rafter length) based on the building's span and roof pitch.
Beyond basic area, this tool itemizes essential trim components: Ridge Caps (for the peak) and Rake Trim (for the sloping edges). It includes a selectable wastage factor to account for cutting scrap, which is critical for metal decking where panels cannot be easily spliced.
Formulas
The calculator determines the Rafter Length (Lr) using the Run (w/2) and Pitch (P).
Multiplier (M) = √1 + (P12)2
Lr = (Width / 2) × M
Area = Lr × Length × 2 (sides)
Waste is applied as Total = Area × (1 + Waste%)
Reference Data
| Pitch (Rise/12) | Angle (°) | Multiplier (Secant) |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 12/12 | 45.0° | 1.414 |